Electrodeposition of magnetic cobalt-nickel alloys



United States Patent New York No Drawing. Filed Aug. 24, 1960, ger. No. 51,525

6 Claims. (Cl. 204-4 This invention relates to electroplating baths for the production of hard magnetic coatings and more particularly to an electrolyte and method for depositing films of cobalt-nickel films having superior magnetic properties for use in magnetic memory devices.

Magnetic materials having high coercive forces find particular application as memory elements in recording drums, discs, tapes, and the like. -In general, a number of plating baths are available in the industry for electroplating these magnetic materials. However, in one or more aspects either the baths or the methods used therewith do not provide entirely satisfactory magnetic deposits. Furthermore, these baths generally operate above room temperature, exhibit a considerable pH drift during plating, form deposits as a result of precipitation in the bath and often require superimposed A.C.-D.C. plating to obtain the requisite high coercive force deposits.

A main object of the present invention is to provide an improved cobalt-nickel plating bath for electroplating high coercive force magnetic materials.

A further object of the invention is to provide an electrolyzable conductive solution including cobalt, nickel, chlOride and sulfamate ions, which solution produces films of cobalt-nickel alloy having high coercive forces.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention.

In accordance with the present invention, an electrolyte is provided for electrodepositing improved films of cobalt-nickel alloys. The ranges of electrolyte constituents and bath parameters are summarized in the table and in the accompanying description thereto.

The cobalt and chloride ions may be conveniently supplied by CoCl .6H O and the chloride ion adjusted with HCI if necessary. The nickel ion is supplied by nickel carbonate and the sulfamate ion by sulfamic acid.

Pure nickel and cobalt, cobalt-nickel alloys or insoluble metals, such as platinum, may be used as the anode. It is desirable that the anode area be twice as large as the cathode area in order to prevent polarization of the anode and to improve the plating current distribution.

A suitable substrate for depositing the magnetic alloy is an aluminum disc which has been given zinc and copper strikes by conventional plating techniques known to those skilled in the art.

An electrolyte bath typical of the present invention was prepared as follows: 60 g. C.P. sulfamic acid was dissolved in about a half liter of water and 30 g. C.P. nickel carbonate was slowly added while stirring until the reaction was completed, as evidenced by the lack of evolution of CO Thereafter, 20 g. C.P. CoCl .6H O was added. The pH was 1.6. Thereupon potassium hydroxide was added to bring the pH up to 6.5 and the solution diluted to a volume of one liter.

In order to aid those skilled in the art in the use of the electrolytic bath of the present invention, in plating hard magnetic coatings, the following details of the plating procedure will now be described.

First, inorganic and organic impurities are removed from the bath constituents. Accordingly, a dummy plating was carried out for about 0.53 ampere-hour per liter of solution before the plating of pure cobalt-nickel alloy films was begun to remove the inorganic impurities. Thereafter, activated charcoal filtration with a wetting agent was used to remove organic impurities.

The actual plating then was carried out, preferably at constant cathode potential, which produces an alloy of uniform composition. The corresponding current density range was about 1025 amps/sq. ft. with 15 a.s.f. being an optimum value. For example, in order to produce films having a thickness of 0.1 mil, a plating potential of 1.7 volts and a current density of 15 a.s. f. was used, the plating being continued for about 10 minutes. Under these conditions the total cathode efliciency was divided between a cobalt cathode efficiency of 65% and a nickel cathode efiiciency of 35%.

The alloy thus produced does not vary more than 1% in composition throughout the entire film during the initial stages of deposition. After 1.7 ampere-hours/liter of plating the alloy composition does change somewhat but the magnetic properties of the deposit remain unaffected. After 2.2 ampere-hours, however, it was necessary to add metallic salts to bring bring the electrolyte up to the original concentration.

The magnetic properties of the films produced from the electrolyte of the present invention may be summarized as follows. For films of 0.1 mil thickness, the coercive force, He, was about 450 oersteds. At 0.06 mil, Hc increased to 600 oersteds. The remanence value, Br, at the latter thickness was 7000 gauss and the squareness ratio Br/Bs, was 0.80.9.

The magnetic and pulse behavior of the alloys of the present invention may be summarized by the following specifications which represent the performance of films deposited from the optimum bath composition under ac tual read-write operation. A magnetic transducer having a gap width of 0.2 mil, a gap length of 6 mils (500 bits/ inch) 100 winding turns to the writing head, 300 Wind ing turns to the reading head and a linear speed of writing of 900 inches per. sec. and a head to film separation of 200 micro-inches was used. The film thickness was 0.08 mils. The output voltage obtained was 68 millivolts with a signal to noise ratio of 18:1. Films deposited from baths having a 1:1 'Ni++/Co++ ratio showed somewhat diminished output signals although within usable range.

A further advantage of the electroplating bath of the present invention resides in the excellent microthrowing power which produces films completely free of pin holes. This ability is further accentuated by first plating at a cathode potential of 4 volts for 15-30 seconds and thereafter at the lower values.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. An electrolyte for electrodepositing hard magnetic 3 coatings composed of cobalt-nickel alloys consisting of between 5-25 g./l. Co++, 5-20 g./l Ni++, 1'0-75 g./l. sulfamate ion and 25-15 g./1. Cl-, the Ni++/Co++ ratio being between 1:1 to 5:1 and the sulfamate ion/ chloride ion ratio being between 0.7:1-3021.

2. The electrolyte according to claim 1 wherein said Co++ concentration is 5-8 g./l., said Ni++ is 10-17 g./l., said sulfarnate ion concentration is 50-70 g./l. and said Cl concentration is 4-10 g./l., the Ni++/Co++ ratio being between 1.2:1-3.4:1 and the sulfamate ion/chloride ion ratio being between 5:1-18:1, said solution adjusted to a pH between 6.0 and 6.8.

3. The electrolyte according to claim 1 wherein said C concentration is g./l., said Ni++ concentration is 15 g./l., said sulfamate ion concentration being 60 g./1. and said (31- concentration being 6 g./l., said solution adjusted to a pH of 6.5.

4. A method of electrodepositing a hard magnetic coating composed of a cobalt-nickel alloy which comprises the steps of eleotrodepositing said alloy from an electrolyte consisting of between 5-25 g./l. Co++, 5-20 g./l. Ni++, 10-75 g./l. sul-famate ion, 2.5- g./l. Cl, the Ni++/ C0++ ratio being between 1:1-5 :1 and the sulfamate ion/ chloride ion ratio being between 0.7:1-3011 at a pH between 5.5 and 7.0 and at a constant plating voltage of between 1.5-4.0 volts.

5. The method according to claim 4 wherein the plating potential is between 1.6-2.0 volts.

6. The method according to claim 4 wherein the plating potential is 1.7 volts and the electrolyte consists of 5 g./l. Co++, 15 g./l. Ni++, g./l. sulfamate ion and 6 g./1. Cl and the pH is 6.5.

References Cited in the file of this patent UNITED STATES PATENTS 2,840,517 Faust et al. June 24, 1958 2,927,066 Schaer Man l, 1960 2,927,889 Clinehens Mar. 8, 1960 OTHER REFERENCES Barrett: Proceedings of the 47th Annual Convention of the American Electroplaters Society, July 1960, pages -175.

Piontelli et 211.: Proceedings of the Third International Conference on Electrodeposition, September 1947, pages 121-125. 

1. AN ELECTROLYTE FOR ELECTRODEPOSITING HARF MAGNETIC COATINGS COMPOSED OF COBALT-NICKEL ALLOYS CONSISTING OF BETWEEN 5-25 G./1. CO++, 5-20 G./1 NI++, 10-75 G./1. SULFAMATE ION AND 2.5-15 G./1. CL-, THE NI++/CO++ RATIO BEING BETWEEN 1:1 TO 5:1 AND THE SULFAMATE ION/CHLORIDE ION RATION BEING BETWEEN 0.7:1-30:1. 